Fixed resistor



G. M. EHLERS FIXED RESISTOR Aug. 27, 1940.

Filed Feb. 27, 1937 INVENTOR.

ATTORNEY.

Patented Aug. 27, 1940 FIXED RESISTOR George M. Ehlers, Milwaukee, Wis., assignor to Globe-Union Inc., Milwaukee, Wis, a corporation of Delaware Application February 27, 1937, Serial No. 128,178

10 Claims. (Cl. 201-154) This invention relates to an improvement in fixed resistors and to a method'of making the same.

One of the principal objects of the invention is toprovide a fixed resistor with an improved lead-wire construction, one wherein the leadwires are effectively connected electrically with the conductive path -of the resistor, securely maintained in position mechanically and this in a construction in which the ends of the resistor are properly insulated. The construction is such that it is convenient to provide resistors of this character with coaxial lead-wires, that is, wires that are alined with the longitudinal axis of the resistor and project beyond the ends thereof.

Another object is to'provide an improved method whereby the lead-wires are properly and efi'ectively organized with the ends of the resistor.

Other objects and advantages reside in certain novel features of the construction, arrangement and combination'of parts which will be hereinafter more fully described and particularly pointed out in the'appended claims, reference being had to. the accompanying drawings forming a part of this specification, and in which:

Figure l' is a fragmentary view in transverse section showing the manner in which the resistor, its lead-wire and end cap are pressed to the mold; I

Figure 2 is a view similar to Figure 1 showing the manner in which the cap is molded over the head .of the lead-wire and the adjacent end of the resistor;

Figure 3 is a View partly in longitudinal vertical section and partly in side elevation showing a resistor embodying the present invention, one of the lead-wires and the disc from which one of the end caps is formed being shown prior to assembly;

Figure 4 is a view similar to Figure 3 but showing the completely assembled device;

Figure 5 isa view in elevation of a modified form of lead-wirea Figure 6 is a view in end elevation of the leafl- Wire shown in Figure 5; v

Figure 7 isan elevation of still another leadwire construction; and

Figure 8 is a view in end elevation of the leadwire shown in Figure '7.

- Referring to the drawings and more'particu- .der the influence of heat and pressure. In lieu and claimed in my application for Electrical resistor elements, filed December 4, 1933, Serial No. 700,872, and my application for Apparatus for and method of making resistor" elements, filed October 1, 1934, Serial No. 746,340.

The ends of the resistor may be coated with a material having a low electrical resistance. This material may be simplyia carbon paint although preferably it is a copper metal spray designated at I2. A lead-wire I3 is provided at each 10 end of the resistor. In the assembly, these leadwires are coaxial 'with the resistor and project outwardly beyond the ends thereof. Each lead-' wire is formed at its inner end with a head it and between the head and the main portion of lo] the lead-wire a shoulder i5 is provided. This is a preferred lead-wire construction although in many instances the particular formation of the lead-wire may be varied. For example, the leadwire designated at it in Figure 7 may be em' 20 ployed. The lead-wire it is provided with 9. lateral projection ii at one end which takes the place of the head l4. Or, as illustrated in Figure 9, a lead-wire l8 may be employed. The leadwire i8 is provided at one end with a circular 25 metal head l9 but the shoulder formation is omitted.

-. In the preferred construction the lead-wires l3 with these shouldered heads are employed and they are held in position by means of molded an trate or embed in' the pores or interstices of the g g end coatings l2 whereby to obtain good electrical contact between these parts.

The invention contemplates the omission of the conductive end coatings l2, the wafers I 2t alone being relied onto provide the desired 'eleces trical contact. And where the heads of the leadin wire are of soft metal the wafers 2! also may be omitted in some instances. a y

Each molded cap 20 is made upof disc of paper, linen, canvas duck, felt, or other similar ma terial which is suitable for impregnation with a thermo-setting resin or a high temperature thermo-plastic, such as Bakelite resin, and capable of being .molded into a sufficiently strong cap un- .55

When the lead-wires are as- 5 k of a resin impregnated disc of material of the character mentioned, a pellet washer of molding powder preformed under pressure may be employed. However, good results are obtained by using a 9 oz. to an 18 oz. canvas duck impregnated with Bakelite resin. The size of the im'' pregnated disc or preformed pellet is dependent upon the desired length of the cap. In this connection it has been found that greater pull-out strength is attained by piercing the hole of the lead-wire in the impregnated washer with a hot pin punch or while the resin is warm in order to prevent tearing of the threads of the fabric due to their being impregnated with a resin which is brittle when cold. Shorter molding time and cleaner molds may be obtained with some of the impregnated'cloths by semi-curing them before molding. .A preferred method of doing this is pierced. When presented to the molding die the discs D lie flush up against the head Hi of its lead-wire so that the shoulder I5 is exposed and presented to the plunger 25 actuated by a spring 21,-or other suitable means, of the molding die. The main portion of the lead-wire is received in the axial bore of the plunger 25 and supported thereby; The resistor R withits end coating {2 and lead wafer ,2! is then pressed against the exposed surface of the head of the lead-wire to forcethe plunger 25 inwardly and thereby cause the disc D to be molded into the'cap 20, as illustrated in Figure 2. The head of the molding die is provided with suitable heating elements 26 so that the caps 20 are molded and cured while in the die.

Good electrical contact between the'lead-wire and the conductive path of the resistor may be insured by the use of the lead' wafers 2| or in' various other ways. For example,the end coating l2 of the resistor or the adjacent portion of the head 14 or both-may be'tinned or a mixture of powdered .solder and flux may be placed on the head M of the lead-wire or on the end coating l2 ofthe resistor'or on both before molding; Then again, instead of providing a separate lead wafer the lead-wire head may be dipped in molten lead prior to being preseed against the end ing. This avoids thinning or weakening of the material making up the insulated end caps as they aresubjected only to sufiicient pressure to form them and mold them in-position. Furthermore, when the plunger applies its force directly to the shoulder, the wire head is forcibly pressed against the end coating or against the interposed lead wafer and any possibility of the resin being extruded from the impregnated discs and forced between the contacting surfaces of the lead-wire head, wafer and end coating is avoided.

During the molding operation the end of the plunger shapes or forms the end of the-insulating resistor cap while the female part 21 of the mold- \ing die forms the side of the cap.

In the process as illustrated, the resistor is held and forced toward the die in any suitable manner so that it' acts as a punch to push the disc D into the heated mold. The process can,

of course, be reversed by holding the resistor stationary and moving the mold.

As has been indicated, many of the advantages of the invention may be realized with modified types of lead-wires, as, for example, those shown in Figures 7 to 10, inclusive. In any event, the dead soft copper wire constituting the lead-wire should be headed in such manner that when the wire is pulled lengthwise it does not unwrap or deform to such extent that it will slip through the hole in the insulating cap. When the insulating caps have been molded and cured they tenaciously adhere to both the head of the wire and the peripheral end portions of the insulating jacket of the resistor proper.

With a resistor constructed in this manner, the lead-wires may be coaxially disposed, are securely held mechanically in position and have good electrical contactwith the conductive path of the resistor. Furthermore, the end caps insulate the ends of the resistor.

The foregoing description of the resistor and process embodying the present invention is to be understood as illustrative rather than restrictive as the present invention contemplates various changes in structure, material and sequence without departing from the spirit of the invention or the scope of the subjoined claims.

The invention claimed is: v

1. The hereindescribed method of making a fixed resistor with lead-wires connected thereto by molded insulating "caps which consists in assembling a resin impregnated disc on a headed lead-wire, pressing the headed end of the leadwire toward the end portion of the fixed resistor,

and subjecting the disc to the action of heat and pressure to form it into a molded and cured cap enclosing and secured to the head of the wire and the end portion of the resistor.

1 2. The hereindescribed, method -of making a fixed resistor with lead-wireshaving headed ends connected thereto by molded insulating caps' which consists in assembling a. disc-like structure including a thermo-setting resin on a leadewire,

pressing the headed end of the lead-wire toward the end portion of a fixed resistor, and subjecting the disc-like structure to the action of heat and pressure to form it into a molded and cured cap, enclosing and secured to the head of the wire and the'end portion of the resistor. I 3. The hereindescribed method of making a 'fixed resistor having a headed and shouldered lead-wire secured to the end of the resistor by a molded insulating cap which consists in assembling a disc-like structure of thermo-setting resin composition on a lead-wire and against the head thereof while leaving the shoulder exposed, presenting-the headed end of the lead-wire to a conductive end portion. of the resistor, and simultaneously subjecting the shoulder and disc to presureand the disc to heat also to force the headed end of the lead-wire toward the end'of the resistor by. virtue of the pressureexertedonthe shoulder and to form the disc into a molded and cured cap'over the head-of the wire and the end of the resistor by virtue of the heat and pressure to which it is subjected. i

4. The hereindescribedmethod' of making a fixed resistor with lead-wires having headed ends connected thereto by molded insulating caps which consists in piercing a resin impregnated disc while the same is'subject to the influence of heat, assembling the pierced disc on a lead-wire,

pressing the headed end of the lead-wire toward the end portion of the resistor and subjecting the disc to the action of heat and pressure to form it into a molded and cured cap over the head of the wire and the end portion of the resistor.

5. A fixed resistor including, a headed lead wire, a soft metal layer between the head of the lead wire and an end of the resistor, said head of the lead wire being pressed into intimate contact with the'soft metal layer, and the soft metal layer being pressed into intimate contact with the adjacent end of the resistor, and a molded insulating cap including a thermo-setting resin composition enclosing and engaging the head of the lead wire, the metal layer and the adjacent portion of the resistor and. securing these parts together by virtue of the force of adhesion set up there-between incidental to. the molding and curing of the cap. v w

6. A fixed resistor comprising a conductive core, an'insulating jacket surrounding the core, conductive coatings on the ends of the resistor and in electrical contact with the core, lead wires having heads engaged with said conductive coatings, and molded caps of insulating material including a thermo-setting resin composition enclosing the heads of the lead wires and said conductive coatings and extending over the end portions of the resistor jacket to insulate the ends of the resistor and to secure the leadwires in firm contact with said conductive coating by V11? tue of the force of adhesion between the engaged portions ofthe molded cap and the resistor;

'7. A fixed resistor having a conductive terminal portion, a conductive coating over said terminal portion and in electrical contact therewith, a headed lead wire having the head thereof engaged with said conductive coating, and a molded cap of enclosing the head of said lead wire and the coated end portion of the resistor and securing the lead wire and resistor together by virtue of the force of adhesion exerted between the molded cap, the lead wire and the resistor.

8. A fixed resistor comprising a conductive core, an insulating jacket surrounding the core, a conductive coating on an end of the resistor and in electrical contact with the core, a lead wire having a head engaged with said coating, and a molded cap constituted of a body of fibrous material impregnated with a thermo-setting resin and engaging and enclosing the head of the lead wire and said conductive coating and the end portion of the jacket of the resistor and securing these parts together by virtue of the force of adhesion set up between the molded cap, the lead wire and the resistor incidental to the molding and curing of the can.

9. A fixed resistor comprising a conductive core, an insulating jacket surrounding the core, a conductive coating applied to an end of the resistor and in electrical contact with the core, a lead wir having a head engaged with said coating, and a molded cap constituted of a textile fabric impregnated with Bakeliteresin and engaging and enclosing the head of the lead wire and said con-- ductive coating and the end portion of the jacket of the resistor and securing these parts together by virtue of the force of adhesion set up between v the molded cap, the lead wire and theresistor ina thermo-setting resin composition engaging and enclosing the head of the lead wire and the coated end portion of the resistor and united to these parts by the force of adhesion and serving to secure the lead wire to the resistor and to insulate the end of the resistor.

GEQRGE M. 

